Leaching of diuron from soil by organic solvent and surfactant

Abstract

Diuron, a phenylurea herbicide, is one of the most pesticides used for pre- or post- emergene weed control in agriculture in Thailand. To remedy biologically or chemically the pesticide contaminated in soil, pretreatment of the contaminated soil including soil washing is often necessary to enhance the leaching of the contaminated compound from soil. This research poject was to study the leaching conditions of diuron from soil sample facilitated by organic solvent or surfactant. Silty-clay type soil from agricultural area was intentionally contaminated with diuron to 100-ppm concentration. A laboratory-scale soil column was then conducted to evaluate the leacing of diuron using various concentrations of organic solvents (methanol, ethanol, n-butanol, sec-butanol, toluene, benzene and acetone) as well as surfactants (SDS, Triton X-100, Tergitol-NP10, Tween 80 and Brij35). The results indicated that 10% (v/v) n-butanol is the most desorbable solvent, exhibiting the leaching efficiency of approximate 50.99±2.32% w/w in diuroncontaminated soil and 72.95%±1.7% w/w in diuron 80-contaminated soil, respectively. The leaching efficiency of diuron from contaminated soil facilitated by surfactant was found to be less effective. The most desorbable surfactant is 20-CMC Triton X-100 with 39.68±2.73% w/w and 45.07±1.19% w/w leaching efficiency for diuron and diuron80, respectively. Aging soil residue studies indicate that time-dependent sorption process are important in leaching diuron in soil. Leaching efficiency using combination of organic solvent (n-butanol) and surfactant (Triton X-100) are increased up to 52.93±2.11% w/w for diuron and 81.01±3.40% w/w for diuron80 compared to that of a washing process with pure organic solvent- or surfactant-aided individually. Diuron leaching efficiency by n-butanol or Triton X-100 decreased when the soil pH was reduced. Leaching of diuron using 10% (v/v) n-butanol was also decreased with increasing ionic strength, while that with 20-CMC Triton X-100 was not strongly affected. The photolytic destruction of diuron using UV/TiO₂ system following a soil washing process was investigated. The data was demonstrated higher rate of diuron photodegradation in leached solution from soil washing process using 10% (v/v) n-butanol over that using other eluent.